Abstract
The objective was to characterise degradation of myo-inositol 1,2,3,4,5,6-hexakis (dihydrogen phosphate) (InsP6) and formation of inositol phosphate (InsP) isomers in different segments of the broiler digestive tract. Influence of an Aspergillus niger (PhyA) and two Escherichia coli-derived (PhyE1 and PhyE2) phytases was also investigated. A total of 600 16-d-old broilers were allocated to forty floor pens (ten pens per treatment). Low-P (5·2g/kg DM) maize-soyabean meal-based diets were fed without (basal diet; BD) or with a phytase added. On day 25, digesta from different digestive tract segments were pooled per segment on a pen-basis, freeze-dried and analysed for P, InsP isomers and the marker TiO2. InsP6 degradation until the lower ileum (74 %) in BD-fed birds showed a high potential of broilers and their gut microbiota to hydrolyse InsP6 in low-P diets. Different InsP patterns in different gut segments suggested the involvement of phosphatases of different origin. Supplemented phytases increased InsP6 hydrolysis in the crop (P<0·01) but not in the lower ileum. Measurements in the crop and proventriculus/gizzard confirmed published in vitro degradation pathways of 3- and 6-phytases for the first time. In the intestinal segments, specifically formed InsP4-5 isomers of supplemented phytases were still present, indicating further activity of these enzymes. Myo-inositol tetrakisphosphate (InsP4) accumulation differed between PhyE1 and PhyE2 compared with PhyA in the anterior segments of the gut (P<0·01). Thus, the hydrolytic cleavage of the first phosphate group is not the only limiting step in phytate degradation in broilers.
Highlights
The objective was to characterise degradation of myo-inositol 1,2,3,4,5,6-hexakis (InsP6) and formation of inositol phosphate (InsP) isomers in different segments of the broiler digestive tract
BD, basal diet; PhyA, BD supplemented with Aspergillus niger 3-phytase, Finase® P; Escherichia coli-derived phytase Quantum® (PhyE1), BD supplemented with Escherichia coli 6-phytase, Quantum®; E. coli-derived phytase Quantum® Blue (PhyE2), BD supplemented with E. coli 6-phytase, Quantum® Blue; InsP3, myo-inositol trisphosphate; ND, not detected; myo-inositol tetrakisphosphate (InsP4), myoinositol tetrakisphosphate; InsP5, myo-inositol pentakisphosphate; InsP6, myo-inositol 1,2,3,4,5,6-hexakis. a–d Mean values in a row with unlike superscript letters were significantly different (P ≤ 0·05; Fisher’s protected least significant difference test)
BD, basal diet; PhyA, BD supplemented with Aspergillus niger 3-phytase, Finase® P; PhyE1, BD supplemented with Escherichia coli 6-phytase, Quantum®; PhyE2, BD supplemented with E. coli 6-phytase, Quantum® Blue; InsP3, myo-inositol trisphosphate; ND, not detected; InsP4, myoinositol tetrakisphosphate; LOQ, limit of quantification; InsP5, myo-inositol pentakisphosphate; InsP6, myo-inositol 1,2,3,4,5,6-hexakis. a–d Mean values in a row with unlike superscript letters were significantly different (P ≤ 0·05; Fisher’s protected least significant difference test)
Summary
The objective was to characterise degradation of myo-inositol 1,2,3,4,5,6-hexakis (dihydrogen phosphate) (InsP6) and formation of inositol phosphate (InsP) isomers in different segments of the broiler digestive tract. InsP6 degradation until the lower ileum (74 %) in BD-fed birds showed a high potential of broilers and their gut microbiota to hydrolyse InsP6 in low-P diets. Phytate represents the primary storage form of P in plant seeds It is defined as any salt of phytic acid (myo-inositol 1,2,3,4,5,6-hexakis (dihydrogen phosphate) or InsP6). We are not aware of any study that has investigated whether this in vitro-based classification is reflected in the pathways of InsP6 degradation in the more complex and variable environment of the digestive tract of broilers
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